In general, a mobile communication system comprises mobile communication devices such as vehicle telephones or portable telephones (hereinafter referred to as mobile stations) and base stations for communicating the mobile stations through radio channels, for example. In this mobile communication system, radio frequency spectrums in different radio communication methods are possibly shared (hereinafter referred to as a frequency sharing) between FDMA/TDMA method (frequency division multiple access/multi-carrier time division multiple access method) and CDMA method (code division multiple access method). In the present situation, the frequency sharing between different codes in CDMA method has been widely used.
In the frequency sharing mobile communication system based on FDMA/TDMA method and CDMA method, the CDMA signal is a shared wave when a desired wave is the FDMA/TDMA signal. In this case, the CDMA signal is the target signal to be removed. In addition, the FDMA/TDMA signal is a shared wave when a desired wave is the CDMA signal. In this case, the FDMA/TDMA signal is the target signal to be removed. Furthermore, in the frequency sharing mobile communication system based on FDMA/TDMA method and TD-CDMA (time divided CDMA) method, the TD-CDMA signal is a shared wave when a desired wave is the FDMA/TDMA signal. In this case, the TD-CDMA signal is the target signal to be removed. In addition, the FDMA/TDMA signal is a shared wave when a desired wave is the TD-CDMA signal. In this case, the FDMA/TDMA signal is the target signal to be removed. Here, TD-CDMA indicates the Time-Divided CDMA or the Time-Slotted CDMA disclosed in the United State patent U.S. Pat. No. 4,799,252 invented by Eizenhoffer, and whose technique is well known in the world.
In the prior art, although the removing method for eliminating shared wave signals in receivers having no diversity function has been disclosed, there is no method for removing shared wave signals in receivers having the diversity function.
In the prior art, there is the technique disclosed in the U.S. patent number U.S. Pat. No. 5,363,403 as the method to remove the shared wave signal when one CDMA signal is a desired wave signal and other CDMA signals are shared wave signals. However, the technique of this patent disclosed no method to eliminate transmission path distortion in a plurality of transmission paths.
In addition, the technique described in the U., patent number U.S. Pat. No. 5,511,068 disclosed an adaptive filter in a time-divided CDMA signal system. However, this U.S. patent disclosed no frequency sharing of the CDMA signal and the TDMA signal in one time slot. In addition, this U.S. patent disclosed no shared wave canceller to remove shared wave signals. Furthermore, it is difficult to apply the conventional technique disclosed in this U.S. patent when a desired wave signal is a digital signal based on FDMA/TDMA method and when a shared wave signal to be removed is the TD-CDMA signal.
Furthermore, the technique described in the Japanese patent laid open publication number JP-A6/141833 disclosed the demodulator having a reverse correlation filter in which one CDMA signal in a plurality of shared CDMA signals is used as a desired wave signal and the distortion of this CDMA signal caused in a plurality of transmission paths is compensated. However, it is difficult to apply this conventional technique to the case that the desired wave signal is the FDMA/TDMA digital signal and the shared wave signal to be removed is the CDMA signal. Furthermore, it is also difficult to apply this conventional technique to the case that the shared wave signal to be removed is the FDMA/TDMA digital signal.
In addition, the Japanese patent laid open publication number JP-A6/244746 disclosed the technique that a replica of the TDMA signal having a large signal power is made and then this TDMA replica is subtracted by the received signal in order to receive the FDMA signal having a small signal power. However, this patent disclosed no technique for CDMA signal and a time shared TDMA signal. In addition to this, this conventional technique described no transmission path simulator to simulate a plurality of transmission paths when replicas are made.
Furthermore, the Japanese patent laid open publication number JP-A8/84105 disclosed the technique of different equalization method related to the frequency diversity method. However, this technique disclosed no TD-CDMA method.
Moreover, the Japanese patent laid open publication number JP-A8/65222 disclosed the technique that a distorted radio wave obtained by using an equalization coefficient used in a radio wave receiving is transmitted. In this technique, the equalization process to be performed on the transmission path is executed when a radio wave is transmitted in advance.
Furthermore, there is the problem in the conventional mobile communication system, which comprises base stations and mobile stations communicating through radio channels, that the quality of CDMA signal or FDMA/TDMA signal as a desired wave signal becomes lower by removing the CDMA signal as a shared wave or FDMA/TDMA signal as a shared wave when the frequency sharing is used between FDMA/TDMA method and CDMA method as different radio wave communication methods.
Moreover, it must be required to construct a mobile communication system having the function of a shared wave canceller for a time-slotted TD-CDMA signal. Further, in order to realize a high quality transmission, it is also required to construct a mobile communication system having a diversity function.
The present invention is made to overcome the above problems. It is an object of the present invention to provide diversity receivers and a frequency sharing mobile communication system having the diversity receivers. These diversity receivers have the diversity function that is capable of removing a CDMA signal, a TD-CDMA signal, or a FDMA/TDMA signal as a shared wave signal without removing a CDMA desired wave signal, a TD-CDMA desired wave signal, or a FDMA/TDMA desired wave signal.